Method and apparatus for requesting system information

ABSTRACT

Provided are a method for requesting, by a user equipment (UE), system information in a wireless communication system and a device supporting the same. The method may include: initiating a random access procedure; requesting system information from a base station (BS) in the initiated random access procedure; receiving, from the BS, a broadcast indication indicating that the requested system information is broadcast in the initiated random access procedure after requesting the system information from the BS; and stopping the initiated random access procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/936,077, filed on Jul. 22, 2020, which is a continuation of U.S.application Ser. No. 16/064,348, filed on Jun. 20, 2018, now U.S. Pat.No. 10,764,929, which is a National Stage application under 35 U.S.C. §371 of International Application No. PCT/KR2018/001067, filed on Jan.24, 2018, which claims the benefit of U.S. Provisional Application No.62/491,360, filed on Apr. 28, 2017 and U.S. Provisional Application No.62/450,568, filed on Jan. 26, 2017. The disclosures of the priorapplications are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method in which a UE requests other systeminformation and a device supporting the same.

Related Art

In order to meet the demand for wireless data traffic soring since the4th generation (4G) communication system came to the market, there areongoing efforts to develop enhanced 5th generation (5G) communicationsystems or pre-5G communication systems. For the reasons, the 5Gcommunication system or pre-5G communication system is called the beyond4G network communication system or post long-term evolution (LTE)system.

System information refers to essential information for communicationbetween a terminal and a base station. In 3GPP LTE, the systeminformation is divided into an MIB (Master Information Block) and an SIB(System Information Block). The MIB is the most essential information.The SIB is subdivided into SIB-x forms according to its importance orcycle. The MIB is transmitted through a PBCH (Physical BroadcastChannel) which is a physical channel. The SIB is common controlinformation and is transmitted through a PDCCH differently from the MIB.

SUMMARY OF THE INVENTION

The number of system information blocks is continuously increasing, andradio resources are required to broadcast a system information block.Thus, as the number of system information blocks increases, the quantityof radio resources required to broadcast a system information block alsoinevitably increases. To transmit continuously increasing systeminformation to a user equipment (UE), it is necessary to propose amethod for acquiring system information that efficiently utilizes radioresources.

According to an embodiment, there is provided a method for requesting,by a UE, system information in a wireless communication system. Themethod may include: initiating a random access procedure; requestingsystem information from a base station (BS) in the initiated randomaccess procedure; receiving, from the BS, a broadcast indicationindicating that the requested system information is broadcast in theinitiated random access procedure after requesting the systeminformation from the BS; and stopping the initiated random accessprocedure.

According to another embodiment, there is provided a UE for requestingsystem information in a wireless communication system. The UE mayinclude: a memory; a transceiver; and a processor to connect the memorywith the transceiver, wherein the processor may: initiate a randomaccess procedure; control the transceiver to request system informationfrom a base station (BS) in the initiated random access procedure;control the transceiver to receive, from the BS, a broadcast indicationindicating that the requested system information is broadcast in theinitiated random access procedure after requesting the systeminformation from the BS; and stop the initiated random access procedure.

A UE can efficiently receive other system information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem.

FIG. 3 shows a user plane of a radio interface protocol of an LTEsystem.

FIG. 4 shows an example of transmitting a master information block(MIB), system information block1 (SIB1), and other SIBs.

FIG. 5 shows an update of system information.

FIG. 6 illustrates a contention-based random access procedure.

FIG. 7 illustrates a non-contention random access procedure.

FIG. 8 shows a procedure for a UE to receive new-type systeminformation.

FIG. 9 shows a method for a UE to acquire updated minimum systeminformation on the basis of a system information modification period.

FIG. 10 shows a procedure for requesting other system information on thebasis of a broadcast indication according to an embodiment of thepresent invention.

FIG. 11 shows a procedure for requesting other system information on thebasis of a broadcast indication according to an embodiment of thepresent invention.

FIG. 12 shows a procedure for requesting other system information on thebasis of a unicast indication according to an embodiment of the presentinvention.

FIG. 13 shows a procedure for requesting other system information on thebasis of a unicast indication according to an embodiment of the presentinvention.

FIG. 14 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

FIG. 15 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

FIG. 16 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

FIG. 17 shows a procedure for a UE to acquire updated minimum systeminformation according to an embodiment of the present invention.

FIG. 18 shows a method for a UE to acquire updated minimum systeminformation according to an embodiment of the present invention.

FIG. 19 is a block diagram illustrating a method for a UE to requestsystem information according to an embodiment of the present invention.

FIG. 20 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE. 5G is an evolution of the LTE-A.

For clarity, the following description will focus on LTE-A/5G. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem. FIG. 3 shows a user plane of a radio interface protocol of anLTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARD) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARM). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

Hereinafter, system information will be described.

FIG. 4 shows an example of transmitting a master information block(MIB), system information block1 (SIB1), and other Ms.

An LTE cell broadcasts basic parameters necessary for the operation ofan IDLE MODE UE and a CONNECTED MODE UE via a plurality of separateinformation blocks. Examples of information blocks include an MIB, SIB1,SIB2, and other SIBs (SIBn).

The MIB includes the most essential parameters needed for a UE to accessa cell. Referring to FIG. 4, an MIB message is broadcast through a BCHaccording to a periodicity of 40 ms, and MIB transmission is repeated inall radio frames within the periodicity of 40 ms. The UE receives an SIBmessage using the parameters received via the MIB.

There are different types of SIBs.

SIB1 includes pieces of information associated with cell access, andparticularly includes scheduling information on other SIBs (SIB2 toSIBn) than SIB1. SIBs having the same transmission periodicity among theSIBs other than SIB1 are transferred via the same system information(SI) message. Thus, scheduling information includes a mappingrelationship between each SIB and an SI message. An SI message istransmitted within an SI window in a time domain, and each SI message isassociated with one SI window. Since SI windows for different pieces ofSI do not overlap, only one SI message is transmitted within an SIwindow. Thus, scheduling information includes the duration of an SIwindow and an SI transmission periodicity. Time/frequency fortransmitting an SI message is determined by dynamic scheduling by a BS.SIB1 is broadcast through a downlink shared channel (DL SCH) accordingto a periodicity of eight radio frames (that is, 80-ms periodicity), andSIB1 is repeatedly retransmitted on a fifth subframe of an SFN-mod-2radio frame within the 80-ms periodicity.

SIB2 includes necessary information for a UE to access a cell. SIB2includes information on an uplink cell bandwidth, a random accessparameter, and an uplink power control parameter.

SIB3 includes cell reselection information. SIB4 includes frequencyinformation on a serving cell and intra-frequency information on aneighboring cell for cell reselection. SIB5 includes frequencyinformation on a different E-UTRA and inter-frequency information on aneighboring cell for cell reselection. SIB6 includes frequencyinformation on a UTRA and information on a UTRA neighboring cell forcell reselection. SIB7 includes frequency information on a GERAN forcell reselection. SIB8 includes information on a neighboring cell.

SIB9 includes a Home eNodeB (HeNB) identifier (ID). SIB10 to SIB12include a public warning message, for example, for earthquake warning.SIB14 is used to support enhanced access barring and controls UEs toaccess a cell. SIB15 includes information needed to receive an MBMS atcontiguous carrier frequencies. SIB16 include GPS time and coordinateduniversal time (UTC)-related information. SIB17 includes RAN auxiliaryinformation.

Not all SIBs are always required to be present. For example, SIB9 is notneeded in a mode where a wireless carrier establishes an HeNB, whileSIB13 is not needed if a cell provides no MBMS.

System information is commonly applied to all UEs accessing a cell, andUEs need to always maintain up-to-date system information to perform anappropriate operation. When system information is changed, UEs need toknow in advance the time the BS transmits new system information. Inorder that a BS and a UE mutually recognize a radio frame period fortransmitting new system information, the concept of BCCH modificationperiod is introduced in “3GPP TS 36.331 v9. 3.0,” which is described indetail.

FIG. 5 shows an update of system information.

Referring to FIG. 5, a BS, which intends to update system information inan (n+1)th modification period, notifies in advance UEs of an update ofsystem information in an nth modification period. A UE, which isnotified the update of the system information in the nth modificationperiod, receives and applies new system information at the verybeginning of the (n+1)th modification period. When an update of systeminformation is scheduled, the BS includes a system informationmodification indicator in a paging message. Generally, a paging messageis a message received by an idle-mode UE. However, since an update ofsystem information is notified through a paging message, aconnected-mode UE also needs to receive a paging message at times and toidentify an update of system information.

Hereinafter, random access will be described.

Random access is used by a UE to obtain uplink synchronization with a BSor to be allocated an uplink radio resource. After power is turned on, aUE obtains downlink synchronization with an initial cell and receivessystem information. Then, the UE acquires, from the system information,a set of available random access preambles and information about a radioresource used for transmission of a random access preamble. The radioresource used for transmission of the random access preamble may bespecified as a radio frame and/or a combination of at least one or moresubframes. The UE transmits a random access preamble randomly selectedfrom the set of random access preambles, and the BS having received therandom access preamble sends a timing alignment (TA) value for uplinksynchronization to the UE through a random access response. Thus, the UEobtains uplink synchronization.

That is, the BS allocates a dedicated random access preamble to aspecific UE, and the UE performs non-contention random access using therandom access preamble. That is, there may be in a process of selectinga random access preamble, contention-based random access in which a UErandomly selects and uses one random access preamble from a particularset and non-contention random access in which only a specific UE isallocated a random access preamble by a BS. Non-contention random accessmay be used for a handover procedure or upon a request by a BS'scommand.

FIG. 6 illustrates a contention-based random access procedure.

Referring to FIG. 6, a UE randomly selects one random access preamblefrom a random access preamble set indicated by system information or ahandover command. The UE selects a radio resource for transmitting therandom access preamble to transmit the selected random access preamble(S610). The radio resource may be a specific subframe, and selecting theradio resource may be selecting a physical random access channel(PRACH).

After transmitting the random access preamble, the UE attempts toreceive a random access response within a random access responsereception window indicated by the system information or the handovercommand and accordingly receives a random access response (S620). Therandom access response may be transmitted in an MAC PDU format, and theMAC PDU may be forwarded via a physical downlink shared channel (PDSCH).Further, a physical downlink control channel (PDCCH) is also forwardedso that the UE properly receives information forwarded via the PDSCH.That is, the PDCCH includes information on the UE receiving the PDSCH,frequency and time information on a radio resource for the PDSCH, and atransmission format for the PDSCH. Once successfully receiving the PDCCHforwarded to the UE, the UE properly receives the random access responsetransmitted via the PDSCH on the basis of the information in the PDCCH.

The random access response may include a random access preambleidentifier (ID), an uplink radio resource (UL grant), a temporarycell-radio network temporary identifier (C-RNTI), and a time alignmentcommand (TAC). Since one random access response may include randomaccess response information for one or more UEs, a random accesspreamble ID may be included to indicate a UE for which a UL grant, atemporary C-RNTI, and a TAC are valid. The random access preamble ID maybe an ID of the random access preamble received by a BS. The TAC may beincluded as information for the UE to adjust uplink synchronization. Therandom access response may be indicated by a random access ID on thePDCCH, that is, a random access-radio network temporary identifier(RA-RNTI).

When the UE receives the random access response valid therefor, the UEprocesses information included in the random access response andperforms scheduled transmission to the BS (S630). That is, the UEapplies the TAC and stores the temporary C-RNTI. Further, the UEtransmits data stored in a buffer of the UE or newly generated data tothe BS using the UL grant. In this case, information to identify the UEneeds to be included, which is for identifying the UE in order to avoida collision since the BS does not determine which UEs perform randomaccess in a contention-based random access process.

There are two methods for including information for identifying a UE.When the UE has a valid cell ID already allocated by a correspondingcell before performing random access, the UE transmits the cell IDthereof through the UL grant. However, when the UE is not allocated avalid cell ID before the random access process, the UE transmits aunique ID thereof (e.g, S-TMSI or random ID). Generally, the unique IDis longer than the cell ID. When the UE transmits the data via the ULgrant, the UE starts a contention resolution timer.

After transmitting the data including the ID of the UE through the ULgrant allocated by receiving the random access response, the UE waitsfor an instruction from the BS to avoid a collision (S640). That is, theUE attempts to receive the PDCCH in order to receive a specific message.There are two proposed methods for receiving a PDCCH. As describedabove, when the ID of the UE transmitted via the UL grant is a cell ID,the UE may attempt to receive the PDCCH using the cell ID of the UE. Inthis case, when the UE receives the PDCCH through the cell ID of the UEbefore the contention resolution timer expires, the UE determines thatrandom access has been normally performed and terminates random access.When the ID transmitted via the UL grant is the unique ID, the UE mayattempt to receive the PDCCH using the temporary C-RNTI included in therandom access response. In this case, when the UE receives the PDCCHthrough the temporary cell ID before the contention resolution timerexpires, the UE identifies data forwarded by the PDSCH indicated by thePDCCH. When the data includes the unique ID of the UE, the UE maydetermine that random access has been normally performed and mayterminate random access.

FIG. 7 illustrates a non-contention random access procedure.

Unlike contention-based random access, non-contention random access maybe terminated when a UE receives a random access response.

Non-contention random access may be initiated by a request, such as ahandover and/or a command from a BS. Here, in these two cases,contention-based random access may also be performed.

The UE is allocated by the BS a designated random access preamble havingno possibility of a collision. The random access preamble may beallocated through a handover command and a PDCCH command (S710).

After being allocated the random access preamble designated for the UE,the UE transmits the random access preamble to the BS (S720).

Upon receiving the random access preamble, the BS transmits a randomaccess response to the UE in response (S730). A procedure associatedwith the random access response has been mentioned above in S620 of FIG.6.

The number of system information blocks is continuously increasing, andradio resources are required to broadcast a system information block.Thus, as the number of system information blocks increases, the quantityof radio resources required to broadcast a system information block alsoinevitably increases. To solve such a problem, new-type systeminformation is proposed.

FIG. 8 shows a procedure for a UE to receive new-type systeminformation.

Referring to FIG. 8, the new-type system information may be divided intominimum system information and other system information. The minimumsystem information may be periodically broadcasted. The minimum systeminformation may include basic information required for initial access toa cell and information for acquiring any other system information thatis provisioned on an on-demand basis or is periodically broadcasted. Theminimum system information may include at least one of a SFN, a list ofPLMNs, a cell ID, a cell camping parameter, and a RACH parameter. When anetwork allows an on-demand mechanism, a parameter required to requestthe other system information may be included in the minimum systeminformation. The other system information may refer to all systeminformation not broadcast in the minimum system information.

A UE may request the network to transmit system information in order toacquire other system information. The other system information may beprovided through broadcasting or may be provided through dedicatedsignaling. When the system information requested by the UE is providedby broadcasting, the UE does not need to switch to the RRC_CONNECTEDmode but needs to acquire scheduling information for acquiring therequested system information in order to acquire the requested systeminformation. However, after the UE requests the network to transmitsystem information, the UE cannot know whether the requested systeminformation is broadcast.

For example, when the network does not broadcast specific systeminformation, the UE in the RRC_IDLE mode may request the specific systeminformation from the network using a RACH procedure. Thereafter, even ifthe network broadcasts the specific system information for any reason,the UE cannot know whether the specific system information isbroadcasted. Therefore, the UE may need to continuously perform the RACHprocedure, which is unnecessary, in order to receive the specific systeminformation. Even if the UE has already received the particular systeminformation from the network in the RACH procedure for any reason, theUE may need to continuously perform the RACH procedure, which isunnecessary, until the RACH procedure is completed. This may cause thewaste of radio resources. Therefore, it is necessary to propose a methodfor acquiring system information that is capable of preventing anunnecessary RACH procedure from being performed.

Further, an existing system information change procedure based on a BCCHmodification period may cause a delay in acquiring requested systeminformation. The BCCH modification period may be referred to as a systeminformation modification period.

FIG. 9 shows a method for a UE to acquire updated minimum systeminformation on the basis of a system information modification period.

Referring to FIG. 9, in step S910, the UE may acquire minimum systeminformation within the system information (SI) window of the minimumsystem information. The UE may determine whether specific systeminformation is broadcast on the basis of scheduling information includedin the minimum system information. The specific system information maybe other system information. When the specific system information is notbroadcast, the UE may request the specific system information from anetwork in step S920. Thereafter, in step S930, the UE may receive aminimum SI change notification. For example, the minimum SI changenotification may be received via a paging message. In step S940, the UEmay read updated minimum system information in the next systeminformation modification period. In step S950, the UE may acquire therequested specific system information. That is, since the UE can readthe updated minimum system information in the next system informationmodification period, a delay of considerable time may occur until the UEacquires the requested system information. Therefore, it is necessary topropose a minimum system information update mechanism to enable the UEto immediately acquire the requested system information from thenetwork.

Hereinafter, a method for receiving system information and a devicesupporting the same will be described in detail according to anembodiment of the present invention.

According to the embodiment of the present invention, a UE may initiatean RACH procedure or a system information request procedure in order torequest other system information. After requesting system information inthe RACH procedure or the system information request procedure, the UEmay receive a system information response in response to the systeminformation request in the RACH procedure or the system informationrequest procedure. The system information response may include abroadcast indication and/or a unicast indication. The unicast indicationmay also be referred to as a dedicated indication. The systeminformation request may be transmitted via a first message, and thesystem information response may be transmitted via a second message.Alternatively, the system information request may be transmitted via athird message, and the system information response may be transmittedvia a fourth message. Alternatively, the system information request maybe transmitted via a first message, and the system information responsemay be transmitted via a fourth message.

For example, when the UE receives a broadcast indication from thenetwork, the UE can know that the requested system information isscheduled to be broadcast in the next SI period. Therefore, the UE maystop the RACH procedure or the system information request procedure.Then, the UE may read minimum system information to receive therequested system information. When the UE receives the broadcastindication from the network, the UE may not perform an RRC state switchto acquire the system information. That is, the UE can receive therequested system information from the network in a broadcast mannerwithout any RRC state switch.

For example, when the UE receives a unicast indication from the network,the UE can know that the requested system information is scheduled to beprovided in a dedicated manner after the RACH procedure or the systeminformation request procedure. Thus, the UE may continue and completethe RACH procedure or the system information request procedure. Afterthe RACH procedure or the system information request procedure, the UEmay enter the RRC_CONNECTED state to acquire the system information.Then, the UE may receive the requested system information from thenetwork in a dedicated manner.

FIG. 10 shows a procedure for requesting other system information on thebasis of a broadcast indication according to an embodiment of thepresent invention.

Referring to FIG. 10, in step S1010, a UE may receive minimum systeminformation from a network. The UE may determine whether other systeminformation is broadcast on the basis of the minimum system information.When the other system information, which the UE is interested inreceiving, is not currently broadcast, the UE may determine to requestthe other system information. To request system information, the UE mayinitiate an RACH procedure or a system information request procedure.

In step S1020, the UE may select a first message resource (i.e.,preamble) corresponding to the other system information of interest.Then, the UE may transmit a system information request using theselected first message resource.

Additionally, after transmitting the system information request, the UEmay start a system information request timer. For example, when thesystem information request timer expires, the UE may attempt to receivenew minimum system information. The new minimum system information maybe received via a second message.

In step S1030, the UE may receive the second message including abroadcast indication. Thus, the UE may expect that the requested systeminformation will be broadcast. When the UE receives the broadcastindication indicating that the requested system information is to bebroadcasted, the UE may stop the RACH procedure or the systeminformation request procedure. Then, the UE may not transmit a thirdmessage. The UE may maintain the current RRC state instead of switchingto the RRC_CONNECTED state. For example, the current RRC state may bethe RRC_IDLE state or the RRC_INACTIVE state.

In step S1040, the UE may read the minimum system information in thenext SI period. The minimum system information may include schedulinginformation on the requested system information.

In step S1050, the UE may receive the requested system information onthe basis of the scheduling information. The requested systeminformation may be received in a broadcast manner.

According to the embodiment of the present invention, the UE can knowthat specific system information is broadcast and thus may stop anongoing RACH process for acquiring system information. Therefore, it ispossible to avoid the waste of radio resources that may occur bycontinuously performing an unnecessary RACH procedure.

FIG. 11 shows a procedure for requesting other system information on thebasis of a broadcast indication according to an embodiment of thepresent invention.

Referring to FIG. 11, in step S1110, a UE may receive minimum systeminformation from a network. The UE may determine whether other systeminformation is broadcast on the basis of the minimum system information.When the other system information, which the UE is interested inreceiving, is not currently broadcast, the UE may determine to requestthe other system information. To request system information, the UE mayinitiate an RACH procedure or a system information request procedure.

In step S1120, the UE may select a first message resource (i.e.,preamble) and may transmit the first message.

In step S1130, the UE may receive a second message.

In step S1140, the UE may transmit a system information request to thenetwork using the third message. Additionally, after transmitting thesystem information request, the UE may start a system informationrequest timer. For example, when the system information request timerexpires, the UE may attempt to receive new minimum system information.The new minimum system information may be received via a fourth message.

In step S1150, the UE may receive the fourth message including abroadcast indication. Thus, the UE may expect that the requested systeminformation will be broadcast. When the UE receives the broadcastindication indicating that the requested system information is to bebroadcasted, the UE may stop the RACH procedure or the systeminformation request procedure. The UE may maintain the current RRC stateinstead of switching to the RRC_CONNECTED state. For example, thecurrent RRC state may be the RRC_IDLE state or the RRC_INACTIVE state.

In step S1160, the UE may read the minimum system information in thenext SI period. The minimum system information may include schedulinginformation on the requested system information.

In step S1170, the UE may receive the requested system information onthe basis of the scheduling information. The requested systeminformation may be received in a broadcast manner.

According to the embodiment of the present invention, the UE can knowthat specific system information is broadcast and thus may stop anongoing RACH process for acquiring system information. Therefore, it ispossible to avoid the waste of radio resources that may occur bycontinuously performing an unnecessary RACH procedure.

FIG. 12 shows a procedure for requesting other system information on thebasis of a unicast indication according to an embodiment of the presentinvention.

Referring to FIG. 12, in step S1210, a UE may receive minimum systeminformation from a network. The UE may determine whether other systeminformation is broadcast on the basis of the minimum system information.When the other system information, which the UE is interested inreceiving, is not currently broadcast, the UE may determine to requestthe other system information. To request system information, the UE mayinitiate an RACH procedure or a system information request procedure.

In step S1220, the UE may select a first message resource (i.e.,preamble) corresponding to the other system information of interest.Then, the UE may transmit a system information request using theselected first message resource. Additionally, after transmitting thesystem information request, the UE may start a system informationrequest timer. For example, when the system information request timerexpires, the UE may attempt to receive new minimum system information.The new minimum system information may be received via a second message.

In step S1230, the UE may receive the second message including abroadcast indication. Thus, the UE may expect that the requested systeminformation will be provided in a dedicated manner.

In step S1240, the UE may transmit a third message. In step S1250, theUE may receive a fourth message. The UE may complete the RACH procedureor the system information request procedure and may switch to theRRC_CONNECTED state.

In step S1260, the UE may receive the requested system information. Therequested system information may be received in the dedicated manner.

FIG. 13 shows a procedure for requesting other system information on thebasis of a unicast indication according to an embodiment of the presentinvention.

Referring to FIG. 13, in step S1310, a UE may receive minimum systeminformation from a network. The UE may determine whether other systeminformation is broadcast on the basis of the minimum system information.When the other system information, which the UE is interested inreceiving, is not currently broadcast, the UE may determine to requestthe other system information. To request system information, the UE mayinitiate an RACH procedure or a system information request procedure.

In step S1320, the UE may select a first message resource (i.e.,preamble) and may transmit the first message.

In step S1330, the UE may receive a second message.

In step S1340, the UE may transmit a system information request to thenetwork using the third message. Additionally, after transmitting thesystem information request, the UE may start a system informationrequest timer. For example, when the system information request timerexpires, the UE may attempt to receive new minimum system information.The new minimum system information may be received via a fourth message.

In step S1350, the UE may receive the fourth message including abroadcast indication. Thus, the UE may expect that the requested systeminformation will be provided in a dedicated manner. The UE may completethe RACH procedure or the system information request procedure and mayswitch to the RRC_CONNECTED state.

In step S1360, the UE may receive the requested system information. Therequested system information may be received in the dedicated manner.

FIG. 14 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

Referring to FIG. 14, in step S1410, the RRC layer of a UE may initiatea system information request procedure for one or more systeminformation messages or one or more system information blocks and maytrigger a random access procedure to request other system information.Additionally, the RRC layer of the UE may start a timer.

In step S1420, the MAC layer of the UE may transmit any one of randomaccess preambles.

In step S1430, after triggering the random access procedure to requestother system information, the RRC layer of the UE may receive therequested other system information (i.e., a system information messageor system information block) at any time.

In step S1440, when the RRC layer of the UE receives the requested othersystem information at any time, the RRC layer of the UE may indicate astop of the triggered random access procedure to the MAC layer of theUE. When the RRC layer of the UE indicates a stop of the triggeredrandom access procedure to the MAC layer of the UE before the initiatedrandom access procedure is completed, the MAC layer of the UE may stopthe triggered random access procedure.

FIG. 15 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

Referring to FIG. 15, in step S1510, the RRC layer of a UE may initiatea system information request procedure for one or more systeminformation messages or one or more system information blocks and maytrigger a random access procedure to request other system informationincluding one or more random access preambles. Additionally, the RRClayer of the UE may start a timer.

In step S1520, the MAC layer of the UE may transmit any one of therandom access preambles.

In step S1530, when the MAC layer of the UE receives a random accessresponse message indicating a stop of the system information request,the MAC layer of the UE may stop the random access procedure.Alternatively, the MAC layer of the UE may consider that the randomaccess procedure is completed. The random access response messageindicating the stop of the system information request may explicitly orimplicitly indicate the system information messages or the systeminformation blocks.

In step S1540, the MAC layer of the UE may stop the random accessprocedure and inform the RRC layer of the UE of the stop of the systeminformation request procedure or the random access procedure. Upon beinginformed of the system information request procedure or the interruptionof the random access procedure, the RRC layer of the UE may stop thesystem information request procedure. Additionally, the RRC layer of theUE may stop the timer.

FIG. 16 shows a procedure for requesting other system informationaccording to an embodiment of the present invention.

Referring to FIG. 16, in step S1610, the RRC layer of a UE may initiatea system information request procedure for one or more systeminformation messages or one or more system information blocks and maytrigger a random access procedure to request other system information.Additionally, the RRC layer of the UE may start a timer.

In step S1620, the MAC layer of the UE may transmit any one of randomaccess preambles.

In step S1630, the MAC layer of the UE may receive a random accessresponse message indicating a random access preamble.

In step S1640, the MAC layer of the UE may transmit a third message on aPUSCH using a UL grant included in a random access response message.

In step S1650, when the MAC layer of the UE receives a fourth messageindicating a stop of the system information request, the MAC layer ofthe UE may stop the random access procedure. Alternatively, the MAClayer of the UE may consider that the random access procedure iscompleted. The fourth message may include at least one of a C-RNTI on aPDCCH of a special cell (SpCell), a minimum system information message,an other system information message, a system information message, and aUE contention resolution identity on a DL-SCH on the PDCCH of the SpCell(Special Cell). The fourth message indicating the stop of the systeminformation request may explicitly or implicitly indicate the systeminformation messages or the system information blocks

In step S1660, the MAC layer of the UE may stop the random accessprocedure and inform the RRC layer of the UE of the stop of the systeminformation request procedure or the random access procedure. Upon beinginformed of the system information request procedure or the interruptionof the random access procedure, the RRC layer of the UE may stop thesystem information request procedure. Additionally, the RRC layer of theUE may stop the timer.

FIG. 17 shows a procedure for a UE to acquire updated minimum systeminformation according to an embodiment of the present invention.

Referring to FIG. 17, in step S1710, the UE may receive minimum systeminformation. The UE may determine other system information that needs tobe requested on the basis of the minimum system information.

In step S1720, the UE may transmit a system information request to anetwork. That is, the UE may request, from the network, the other systeminformation that needs to be requested.

In step S1730, the UE may receive updated minimum system information.According to the embodiment of the present invention, the UE may receivethe updated minimum system information using three methods.

According to a first option, after the UE transmits the systeminformation request or receives an indication that the requested systeminformation is to be broadcasted, the UE may read the minimum systeminformation transmits in the next short message system informationmodification period. In this case, the UE may not receive a systeminformation change notification. Although there is no system informationchange notification, the UE may expect that the minimum systeminformation will be updated after the system information request. Thus,the UE may read the minimum system information in the next short systeminformation modification period without receiving a system informationchange notification.

According to a second option, after the UE transmits the systeminformation request or receives an indication that the requested systeminformation is to be broadcasted, the UE may read minimum systeminformation from the next transmission of the minimum system informationuntil scheduling information on the requested system information isincluded in the minimum system information. That is, the UE may continueto read the minimum system information until the scheduling informationon the requested system information is included in the minimum systeminformation.

According to a third option, after the UE transmits the systeminformation request, the UE may start a system information requesttimer. When the system information request timer expires, the UE mayread minimum system information from the first transmission of theminimum system information. When the minimum system information does notinclude scheduling information on the requested system information, theUE may read minimum system information transmitted next.

In step S1740, when the UE acquires minimum system information includingscheduling information on the requested system information, the UE mayread the requested system information in the first system informationwindow of the requested system information. Preferably, the change ofinformation other than the scheduling information on the requestedsystem information may not be allowed within the same system informationmodification period. When the information other than the schedulinginformation on the other system information is changed, the UE mayacquire updated minimum system information according to a legacy systeminformation change procedure. That is, when the information other thanthe scheduling information on the other system information is changed,the UE may acquire updated minimum system information on the basis of asystem information modification period or a system information changenotification.

According to the embodiment of the present invention, after requestingsystem information, the UE does not need to wait until the next systeminformation modification period in order to acquire updated minimumsystem information including scheduling information on the requestedother system information. Further, after requesting the systeminformation, the UE does not need to receive a system information changenotification in order to check whether minimum system information isupdated. Thus, compared to a conventional procedure, the UE can quicklyacquire requested other system information.

FIG. 18 shows a method for a UE to acquire updated minimum systeminformation according to an embodiment of the present invention.Specifically, (a) of FIG. 18 shows a method for a UE to acquire updatedminimum system information according to the first option, (b) of FIG. 18shows a method for a UE to acquire updated minimum system informationaccording to the second option, and (c) of FIG. 18 shows a method for aUE to acquire updated minimum system information according to the thirdoption.

Referring to (a) of FIG. 18, in step S1801, the UE may acquire minimumsystem information in an SI window for the minimum system information.The UE may determine whether specific system information is broadcast onthe basis of scheduling information included in the minimum systeminformation. The specific system information may be other systeminformation. When the specific system information is not broadcast, theUE may request the specific system information from a network in stepS1802. The UE may expect that scheduling information on the requestedsystem information will be included in the minimum system information inthe next short system information modification period. A configurationof the short system information modification period may be included inthe minimum system information. The configuration of the short systeminformation modification period may include the length of the shortsystem information modification period and an offset of the short systeminformation modification period. In step S1803, the UE may read updatedminimum system information in the next short system informationmodification period. In step S1804, the UE may acquire the requestedsystem information.

Referring to (b) of FIG. 18, in step S1811, the UE may acquire minimumsystem information in an SI window for the minimum system information.The UE may determine whether specific system information is broadcast onthe basis of scheduling information included in the minimum systeminformation. The specific system information may be other systeminformation. When the specific system information is not broadcast, theUE may request the specific system information from a network in stepS1812. The UE may expect that scheduling information on the requestedsystem information will be immediately included in the minimum systeminformation. In step S1813, the UE may read the minimum systeminformation in the next transmission of the minimum system information.However, it is assumed that the minimum system information has not yetbeen updated. That is, it is assumed that the minimum system informationdoes not yet include the scheduling information on the requested systeminformation. In step S1814, the UE may re-read minimum systeminformation. The minimum system information re-read by the UE has beenupdated and may include the scheduling information on the requestedsystem information. In step S1815, the UE may acquire the requestedsystem information.

Referring to (c) of FIG. 18, in step S1821, the UE may acquire minimumsystem information in an SI window for the minimum system information.The UE may determine whether specific system information is broadcast onthe basis of scheduling information included in the minimum systeminformation. The specific system information may be other systeminformation. When the specific system information is not broadcast, theUE may request the specific system information from a network in stepS1802. The UE may expect that scheduling information on the requestedsystem information will be immediately included in the minimum systeminformation. Additionally, after requesting the system information, theUE may start a system information request timer. Preferably, the valueof the system information request timer may be included in the minimumsystem information. In step S1823, the system information request timermay expire. After the system information request timer expires, the UEmay read minimum system information in the first transmission of theminimum system information in step S1824. The minimum system informationhas been updated and may include the scheduling information on therequested system information. In step S1825, the UE may acquire therequested system information.

FIG. 19 is a block diagram illustrating a method for a UE to requestsystem information according to an embodiment of the present invention.

Referring to FIG. 19, in step S1910, the UE may initiate a random accessprocedure.

In step S1920, the UE may request system information from a BS in theinitiated random access procedure. The system information may berequested from the BS via a random access preamble message. The systeminformation may be requested from the BS via a scheduled transmissionmessage. The system information may be other system information.

In step S1930, after requesting the system information from the BS, theUE may receive, from the BS, a broadcast indication indicating that therequested system information is broadcast in the initiated random accessprocedure. The broadcast indication indicating that the requested systeminformation is broadcast may be received from the BS via second minimumsystem information. The second minimum system information may includescheduling information on the requested system information. Thebroadcast indication may be received from the BS via a random accessresponse message. The broadcast indication may be received from the BSvia a collision resolution message.

In step S1940, the UE may stop the initiated random access procedure.After the broadcast indication indicating that the requested systeminformation is broadcast is received from the BS, the initiated randomaccess procedure may be stopped. Alternatively, after the requestedsystem information is received from the BS, the initiated random accessprocedure may be stopped.

In addition, the UE may receive first minimum system information fromthe BS. The first minimum system information may indicate that thesystem information is not broadcast. When the first minimum systeminformation indicates that the system information is not broadcast, thesystem information may be requested from the BS in the initiated randomaccess procedure.

Further, the UE may receive the requested system information from the BSon the basis of the scheduling information on the requested systeminformation, without changing the RRC state of the UE.

Additionally, after requesting the system information from the BS, theUE may start a system information request timer. In addition, when thesystem information request timer expires, the UE may receive the secondminimum system information from the BS. The broadcast indicationindicating that the requested system information is broadcast may bereceived from the BS via the second minimum system information.

FIG. 20 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

A BS 2000 includes a processor 2001, a memory 2002 and a transceiver2003. The memory 2002 is connected to the processor 2001, and storesvarious information for driving the processor 2001. The transceiver 2003is connected to the processor 2001, and transmits and/or receives radiosignals. The processor 2001 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the basestation may be implemented by the processor 2001.

A UE 2010 includes a processor 2011, a memory 2012 and a transceiver2013. The memory 2012 is connected to the processor 2011, and storesvarious information for driving the processor 2011. The transceiver 2013is connected to the processor 2011, and transmits and/or receives radiosignals. The processor 2011 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the UE may beimplemented by the processor 2011.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The transceiver may include abase-band circuit for processing a wireless signal. When the embodimentis implemented in software, the aforementioned methods can beimplemented with a module (i.e., process, function, etc.) for performingthe aforementioned functions. The module may be stored in the memory andmay be performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Various methods based on the present specification have been describedby referring to drawings and reference numerals given in the drawings onthe basis of the aforementioned examples. Although each method describesmultiple steps or blocks in a specific order for convenience ofexplanation, the invention disclosed in the claims is not limited to theorder of the steps or blocks, and each step or block can be implementedin a different order, or can be performed simultaneously with othersteps or blocks. In addition, those ordinarily skilled in the art canknow that the invention is not limited to each of the steps or blocks,and at least one different step can be added or deleted withoutdeparting from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should benoted that those ordinarily skilled in the art know that all possiblecombinations of examples cannot be explained, and also know that variouscombinations can be derived from the technique of the presentspecification. Therefore, the protection scope of the invention shouldbe determined by combining various examples described in the detailedexplanation, without departing from the scope of the following claims.

What is claimed is:
 1. A method performed by a wireless device operatingin a wireless communication system, the method comprising: receiving,from a base station (BS), minimum system information broadcastperiodically; triggering a random access procedure for requestingon-demand system information; transmitting, to the BS, a random accesspreamble as a first part of the random access procedure for requestingthe on-demand system information; receiving, from the BS, a randomaccess response as a second part of the random access procedure, therandom access response being responsive to the random access preamble;considering the random access procedure completed based on the randomaccess response, wherein an indication is provided by a medium accesscontrol (MAC) layer of the wireless device to a radio resource control(RRC) layer of the wireless device, the indication being responsive tothe triggered random access procedure for requesting the on-demandsystem information.
 2. The method of claim 1, further comprising:receiving, from the BS, the on-demand system information based on therandom access response.
 3. The method of claim 1, further comprising:receiving, from the BS, a random access channel (RACH) configuration. 4.The method of claim 3, wherein the random access preamble is transmittedafter receiving the RACH configuration.
 5. The method of claim 1,wherein the triggered random access procedure is stopped based on therandom access response.
 6. A wireless device configured to operate in awireless communication system, the wireless device comprising: at leastone transceiver; at least one processor; and at least one computermemory operably connected to the at least one processor and storinginstructions that, based on being executed by the at least oneprocessor, perform operations comprising: receiving, from a base station(BS), minimum system information broadcast periodically; triggering arandom access procedure for requesting on-demand system information;transmitting, to the BS, a random access preamble as a first part of therandom access procedure for requesting the on-demand system information;receiving, from the BS, a random access response as a second part of therandom access procedure, the random access response being responsive tothe random access preamble; considering the random access procedurecompleted based on the random access response, wherein an indication isprovided by a medium access control (MAC) layer of the wireless deviceto a radio resource control (RRC) layer of the wireless device, theindication being responsive to the triggered random access procedure forrequesting the on-demand system information.
 7. The wireless device ofclaim 6, wherein the operations further comprising: receiving, from theBS, the on-demand system information based on the random accessresponse.
 8. The wireless device of claim 6, wherein the operationsfurther comprising: receiving, from the BS, a random access channel(RACH) configuration.
 9. The wireless device of claim 8, wherein therandom access preamble is transmitted after receiving the RACHconfiguration.
 10. The wireless device of claim 6, wherein the triggeredrandom access procedure is stopped based on the random access response.11. A processing apparatus for a wireless device configured to operatein a wireless communication system, the processing apparatus comprising:at least one processor; and at least one computer memory operablyconnected to the at least one processor and storing instructions that,based on being executed by the at least one processor, performoperations comprising: receiving minimum system information broadcastperiodically; triggering a random access procedure for requestingon-demand system information; transmitting a random access preamble as afirst part of the random access procedure for requesting the on-demandsystem information; receiving a random access response as a second partof the random access procedure, the random access response beingresponsive to the random access preamble; considering the random accessprocedure completed based on the random access response, wherein anindication is provided by a medium access control (MAC) layer of thewireless device to a radio resource control (RRC) layer of the wirelessdevice, the indication being responsive to the triggered random accessprocedure for requesting the on-demand system information.